Re: [PATCH v4 10/10] iommu/arm-smmu-v3: Allow sharing domain across SMMUs

Jason Gunthorpe
2026-04-10T00:32:41Z

On Thu, Mar 19, 2026 at 12:51:56PM -0700, Nicolin Chen wrote:
> @@ -987,6 +988,32 @@ struct arm_smmu_nested_domain {
> __le64 ste[2];
> };
>
> +static inline bool
> +arm_smmu_domain_can_share(struct arm_smmu_domain *smmu_domain,
> + struct arm_smmu_device *new_smmu)
> +{

Probably a bit big for an inline

> + struct io_pgtable *pgtbl =
> + io_pgtable_ops_to_pgtable(smmu_domain->pgtbl_ops);
> +
> + if (pgtbl->fmt == ARM_64_LPAE_S1 &&
> + !(new_smmu->features & ARM_SMMU_FEAT_TRANS_S1))
> + return false;
> + if (pgtbl->fmt == ARM_64_LPAE_S2 &&
> + !(new_smmu->features & ARM_SMMU_FEAT_TRANS_S2))
> + return false;
> + if (pgtbl->cfg.pgsize_bitmap & ~new_smmu->pgsize_bitmap)
> + return false;

I think this should check the lowest set bit in the
domain->pgsize_bitmap is set in new_smmu->pgsize_bitmap

ie that the selected tg is supported.

The cfg.pgsize_bitmap is something a little different IIRC

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason